Reduction of aromatic nitrogen compounds



REDUCTIBN F AROMATIC NITROGEN COMPOUNDS Allen Walter Sogn,Williamsville, N. Y., assignor to Allied Chemical & Dye Corporation, NewYork, N. Y., a corporation of New York No Drawing. Application August 6,1954,

Serial No. 448,377

19 Claims. (Cl. 260-569) This invention relates to improvements in thereductron of aromatic nitrogen compounds containing nitrogen in areducible form as a substituent of a benzene nucleus tion. A particularfeature of the present invention re-: lates to an improved process forthe reduction of such aromatic nitrogen compounds which also contain asa nuclear substituent at least one labile halogen atom, and particularlya labile chlorine atom. 1

The primary object of the present invention is to provide an improvedmethod of carrying out the reduction of aromatic nitrogen compounds ofthe type referred to above by means of reducing sugars and causticalkalis.

Further objects of the present invention are to provide improvements inreduction of water-insoluble aromatic nitrogen compounds containingnitrogen in a reducible form as a substituent of a benzene nucleus at astage of oxidation higher than the hydrazo stage but lower than thenitro stage, whereby the production of azo and hydrazo compounds iseffected under mild reaction'conditions and the production of primaryamines is repressed;. to provide improvements in reductions of said typewhereby the reducing power of reducing sugars and caustic alkalis, andespecially of dextrose and sodium hydroxide, is enhanced and otheradvantages are secured; and to provide a process for the production ofaromatic hydrazo compounds by reduction of aromatic nitro compounds andother reducible aromatic nitrogen compounds with" reducing sugars andcaustic alkalis under moderate conditions and in simple apparatus.

Another object of the present invention is to provide an improved methodfor the reduction of aromatic nitrogen compounds containing nitrogen ina reducible form as a substituent of a benzene nucleus at a higher stageof oxidation than the hydrazo stage, especially azoxy and azo compoundsof said type, and further containing as a substituent at least onelabile halogen atom, especially a labile chlorine atom.

A specific object of the present invention is to pronited States Patent"vide an improved process for the alkaline reduction Of' mononucleararomatic mononitro compounds containing halogen, and especiallychlorine, as a nuclear substituent ortho to the nitro group, andespeciallyortho-chloro-- nitrobenzene and reduction products thereof.

2,7'94,0 4 7 Patented May 28, 1957 "ice Additional objects in part willbeobvious and in part will appear hereinafter.

The reduction of aromatic nitrogen compounds of the above type for theproduction of aromatic hydrazo compounds, particularly in connectionwith the manufacture of benzidine and related diamino-biphenylcompounds, presents a number of problems in view of the nature of saidcompounds and the intermediate products formed. Unless precautions aretaken, the reduction products are mainly aniline or other primaryamines, and/or large quantifies of hydrogen are evolved. V

Thus, under acid conditions, the products are mainly primary amines.Alkaline reducing agents, such as alkali metal alcoholates, ordinarilyare not sufliciently efiective reducing agents to carry the reductionbeyond the azoxy stage unless high temperatures and pressures areemployed. Dextrose and caustic alkalis are inefficient; they lead toformation of amines and other by-products and ordinarily are notsufliciently eifective to carry ,the reduction of the nitro compoundssubstantially beyond the azoxy stage. Zinc, commonly employed withcaustic alkalis, is expensive and requires additional processingoperations to effect removal of the zinc oxide formed as a by-product.

The reduction of reducible aromatic nitrogen-containing compounds havinga labile halogen (e. g. chloro) substituent presents a special problemowing to the reactivity of the labile halogen atom. While it was knownto reduce other aromatic nitrogen compounds to azoxy compounds byheating with metal alcoholates in strongly alkaline media, such reducingagents cannot be employed economically for the reduction of reduciblearomatic nitrogen compounds containing a labile halogen substituentbecause the halogen atom reacts with the metal alcoholate to formethers. Therefore, the reduction of ortho-halogen nitro aromaticcompounds and similar reducible aromatic nitrogen compounds having alabile halogen atom as a substituent, as well as the corresponding azoxyand azo.

compounds, has been carried out by means of zinc and caustic alkali orsimilar reducing agents. For example, U. S. Patent 2,383,134 describes aprocess in which a nitro compound is reduced to the azoxy stage by meansof dextrose and sodium hydroxide and then further reduced to the hydrazostage by means of zinc and sodium hydroxide.

According to one feature of the present invention, the reduction ofreducible aromatic nitrogen compounds of the above type by means of areducing sugar and a caustic alkali is carried out in a reaction mediumin which a naphthoquinoid reduction promotor has been incorporated. Ihave discovered that the inclusion of a naphthoquinoid reductionpromoter in the reaction mixture has a modifying effect upon thereducing action of the reducing sugar whereby a number of benefits aresecured. Thus I have found that the reducing power of reducingsugar-caustic alkali reducing agents is increased materially, thereduction of reducible aromatic nitrogen compounds of the above typeproceeds more rapidly, under milder reaction conditions and/ or to ahigher stage of reduction, than in the absence of the naphthoquinoidreduction promoter.

According to another feature of the present invention, the'-reduction ofaromatic nitrogen compounds of the aforesaidtype, wherein the nitrogenis at a higher stage of oxidationthan the hydrazo stage but not higherthan 2 the azoxy stage, by means of a reducing sugar and caustic alkaliis carried out in a reaction medium which contains a water-miscibleorganic solvent, more partrcularly a lower monohydric alcohol (such asmethanol, ethanol, or a propanol), and especially methanol. I havediscovered, when the reduction of aromatic nitrogen compounds of suchtype, and especially aromatic azo compounds of such type, by means of areducing sugar and a caustic alkali is carried out in such a reactionmedlum, it becomes feasible to produce hydrazobenzenes from azoxyandazobenzenes by means of caustic alkalireducing sugar reducing agents.

ccording to the preferred embodiment'of the present invention, andespecially for the efficient production of reduction products of a lowerstage of oxidation (greater stage of reduction) than the -azoxy stageunder ordinary temperature and pressure conditions, the reduction of thereducible aromatic nitrogen compound by means of a reducing sugar and acaustic alkali (especially'dextrose and sodium hydroxide) is carried outin a reaction medlum in which one or more naphthoquinoid reductionpromoters have been incorporated, preferablyinsmall amount, and whichcontains a water-miscible organic solvent, especially a lower monohydricalcohol, and preferably methanol.

I have discovered that the inclusion in the reaction mixture of-both awater-miscible organic solvent, such as a lower alcohol, and anaphthoquinoid reduction promoter makes possible theobtainment of higheryields of the desired azoxy, azo and/or hydrazo compounds with lessformation of undesired by-products and with the use of much lessreducing sugar, as compared with similar reductions carried out in theirabsence. The reduction can be carried completely through to the hydrazostage Without requiring drastic reaction conditions of temperatureandpressure. Even when a lower alcohol is employed as the solvent,'thereaction can be carried out so rapidly and under such mild reactionconditions that themain reducing effect is brought about by the reducingsugar rather than by the alcohol. Furthermore, when the reduciblearomatic nitrogen compound contains a labile halogen substituent, littleether formation occurs under the mild reaction conditions at which thereduction takes place, notwithstanding the presence of the alcohol andcaustic alkali.

The class of naphthoquinoid reduction promoters employed in the practiceof the present invention includes all of the various naphthoquinones,derivatives, and related compounds which are effective as reductionpro-.

motors in the reduction-of said aromatic nitrogen compounds by alcoholiccaustic alkali, specifically sodium methylate.

As disclosed in my Patent No. 2,645,636, the addition of naphthoquinonesor various derivatives thereof to.

the reaction medium, in the reduction of reducible aromatic nitrogencompounds of the type referred to above by the action of metalalcoholates, especially alkali metal alcoholates and particularly asodium methylate reaction medium resulting from the reaction of sodium.

hydroxide and methanol, exerts a beneficial promoting effect upon thereaction whereby the reaction is accelerated' and/or the reduction canbe carried to a higher stage of reduction without requiring drasticoperating conditions, and other benefits are secured. As disclosed insaid patent, various naphthoquinones, and especially1,4-naphthoquinones, and various derivatives thereof exert thisbeneficial reduction promoting effect; including substitutednaphthoquinones (such as, those in which one or'more of the hydrogenatoms of the naphthoquinone nucleus are substituted by another atom orradical), addition compounds of such naphthoquinones (such as,Withbisulfites and heavy metal salts), functional derivatives ofsuch'naphthoquinones (for example, imides, oximes,-seniicarbazones and*hydrazones), and tautomers and isomers capable of isomerizing to'such-naphthoa'toms 0f the 'quinone nucleus other than those forming "are3 quinones. Specific illustrative compounds of said type1,4-naphthoquinone, 1,2-naphthoquinone, 2,3-dichloro 1,4 naphthoquinone,2-methyl-1,4-naphthoquinone, 2 anilino 1,4 naphthoquinone,2-hydroXy-1,4- naphthoquinone, 1,4 naphthoquinone 2-sulfonic acid,1,4-naphthoquinone oxime, and the sodium bisulfite addition product of1,4-naphthoquinone.

I have also found that certain of such derivatives are speciallyeffective as reduction promoters for such reductions, namely, condensednuclear substitution derivatives of naphthoquinones in which aheterocyclic nucleus is condensed with the quinone nucleus of thenaphthoquinone through two adjacent carbon atoms of said nucleus, andespecially, 1,4-naphthoquinone-furans and -thiofurans (for example,dinaphtho(2,l,2',3')furan-8,13- dione,dinaphtho(1,2,2',3)furan-7,l2-dione, naphtho( 2, 3-b furan-4,9-dione,2-methylnaphtho( 2,3-b furan-4,9- dione,benzo(b)naphtho(2,3-d)furan-6,ll-dione, benzo (b)1Jhiophanthrene-6,11dione, 8 chlorobenzo(b)thiophanthrene-6,l l-dione, 3-hydroxybenzo bnaphtho (2,3- d)furan-6,l1-dione, 8,13-diacetoxy dinaphtho(2,1,2',3)furan, 3 methoxydinaphtho(2,l,2,3')furan-8,l3-dione,dinaphth0(1,2,2',3')furan-7,12-dione-5-sulfonic acid,dinaphtho(2,3,2',3')furan-5,7,12,13-tetrone, dinaphtho(2,

l,2,3)thiophene 8,13 dione,5-chlorodinaphtho(1,2,2,

3)furan-7,12-diol), as disclosed in my-application Serial No. 522,164,filed July 14, 1955.

Furthermore, as disclosed in my Patent No. 2,684,358, this reductionpromoting effect upon the reducing action of alkali metal alcoholates onreducible aromatic nitrogen compounds of the type referred to above isalso brought about by quinoid hydroxynaphthalene compounds; namely,hydroxynaphthalenes having a total of at least two nuclear substituentsof which not more than twoare hydroxyl groups and of which substituentstwo are in the same benzene ring of the naphthalene nucleus in quinoidrelation to each other,'one of said substituents in quinoid relationbeing a hydroxyl group and the other of said substituents in quinoidrelation being a hydroxyl group or an amine radical, functionalderivatives of such compounds, and substituted derivatives of suchcompounds (for example, 1,4-dihydroxy-naphthalene,1,4-dihydroxynaphthalene 2 sulfonic acid, 4-amino-1-hydroxy-naphthalene,4-amino-1-hydroxy-naphthalene-Z-sulfonic acid,

' Z-amino-l-hydroxy-naphthalene, 2,3-dihydroxy-naphthalene,2,3-dihydroxy-naphthalene-G-sulfonic acid, l-amino-2-hydroxy-naphthalene, l-amino-Z-hydroxy-naphthaleue- 4-sulfonic acid,4-phenylamino-l-hydroxynaphthalene).

And, as disclosed in application Serial No. 290,089,

filed May 26,1952, by Francis W. Cashion, a special classofnaphthoquinone addition products particularly useful for promoting thereducing action of alkali metal alcoholates on said-reducible aromaticnitrogen compounds are the addition products of naphthoquinones withsulfiding compounds; such as, hydrogen sulfide, monosulfides,hydrosulfides, polysulfides, thiosulfates, thiocarbonates,hydrosulfites, thiocyanates and related compounds which react withquinones to form reduction products containing, as a nuclearsubstituent, sulfur to -which is linked a cation, sulfur or a carbonatom, which sulfiding compounds when in the salt form have the cation inthe form of a light metal, and especially an alkali metal, or ammonia oran organic amine (for example, addition products of 1,4-naphthoquinonewith sodium sulfide, ammonium sulfide, sodium hydrosulfide,

and ammonium hydrosulfide).

As disclosed in application Serial No. 450,784, filed August 18, 1954,by Leigh C. Anderson and-Chester E. Smith, Jr., the reduction promotingeffect upon the reducing action of alkali metal alcoholates on reduciblearomatic nitrogen compounds of the type referred to above is alsobrought about by ortho-cycloalkano-benzequinoid compounds, such asorthocycloalkano-benzoquinones (benzoquinones in which two adjacentcarbon part of the carbonyl groups are linked respectively to the endcarbon atoms of a chain of at least 3 carbon atoms, and preferably 4carbon atoms, of which at least 2 are saturated carbon atoms and theothers may be unsaturatedwhether free from other substituents in thebenzene nucleus besides the carbonyl oxygen atoms and .the cycloalkanoradical, or containing additional 'substitucuts in the benzene nucleuswherein one or more of the hydrogen atoms of the benzene nucleus issubstituted by another atom or radical); addition compounds of suchbenzoquinones, e. g., with hydroquinones, bisulfites, heavy metal salts,sulfiding compounds, etc.; functional derivatives and tautomeric formsof such benzoquinones capable of isomerizing to such benzoquinones, e.g., imides, oximes, semicarbazones and hydrazones; and hydroquinonescorresponding to such benzoquinones (for example,2,3-cyclopropano-1,4-benzoquinone, 2,3-cyclobutano-1,4-benzoquinone,2,3-cyclobutan-benzohydroquinone,6-chloro-2,3-cyclobutano-1,4-benzoquinone, 2,3-cyclobuteno-l,4-benzoquinone, 2,3 -cyclobutano-l,4-benzohydroquinonediacetate, 2,3-(2-chloro-cyclobuteno)-1,4- benzohydroquinone). V

And, as disclosed in application Serial No. 448,378, filed of even dateherewith, by A. V. Erkkila, effective reduction promoting influence uponthe reducing action of alkali metal alcoholates on reducible aromaticnitrogen compounds of the type referred to above is produced by certaincondensed polynuclear dioxy compounds (diketones, hydroxy-ketones,addition compounds thereof such as with the bisulfites disclosed in myPatent No. 2,645,636--functional derivatives, and tautomeric formsthereof capable of isomerizing thereto, and corresponding dihydroxycompounds in which the keto groups are replaced by groups) which containat least 10 nuclear carbon atoms; namely, those in which one of thenuclei consists of a 6-carbon atom alicyclic dioxy radical having theoxy substituents in quinoid relation to each other, at least 2 of thenuclear carbon atoms of said dioxy radical other than those bearing theoxy substituents being saturated carbon atoms (for example, condensedpolynuclear derivatives of cyclohexandiones, cyclohexendiones,cyclohexandiols and cyclohexendiols, having the oxy groups in 1,2- or1,4- relation, such as 1,2- and 1,4-dioxy-naphthanes and especially1,4-naphthandiones and 1,4-naphthandiols). Specific illustrativeexamples of compounds of said type are: n -naphthantriene-1,4-dione, A-naphthandienemoter as employed herein, including the claims, denotesand includes all of the foregoing naphthoquinones, derivatives andrelated compounds.

In the practice of the preferred embodiment of the present invention,the aromatic nitrogen compound is subjected to the reducing action of amixture of a reducing sugar and a caustic alkali, preferably dextroseand sodium hydroxide, dissolved or suspended in a suitable reactionmedium, such as water, a water-miscible solvent, or an aqueous solutionof such solvent, to which one or a plurality of naphthoquinoid reductionpromoters also have been added or otherwise incorporated, preferably insmall amount.

According to the preferred procedure, one of the reactants (the causticalkali, the reducing sugar, the aromatic nitrogen compound, or thepromoter) is added gradually to a mixture of the other reactants. Forexample, the naphthoquinoid reduction promoter, the aro- 3 maticnitrogen compound to be reduced and the caustic alkali (or reducingsugar) are preferably mixed with water, a water-miscible solvent, or anaqueous solution of the solvent, and the reducing sugar (or causticalkali) is added in small portions to the resulting mixture. (Additionof the caustic alkali to the other reactants leads to a slightly higheryield of reduction product; addition of --the reducing sugar to theother reactants is simpler.)

This procedure makes possible, in a simple and eifective manner, controlof the strongly exothermic reaction, which is an advantage in commercialscale operation.

Various reducing sugars can be employed in the practice of the presentinvention. Thus, suitable reducing sugars include glycol aldehyde,glycerol aldehyde, erythrose, arabinose, xylose, fructose, invert sugar,galactose, and dextrose (glucose). Dextrose is preferred in view of itsefiiciency, ready availability, and low cost.

The process of the present invention can be carried out in an aqueousmedium under ordinary temperatures and pressures, but the reductionusually does not proceed as energetically nor to as low a stage ofoxidation as when the reduction reaction medium comprises awater-miscible organic solvent, such as a monohydric alcohol containing1 to 3 carbon atoms and preferably methanol. When a water-misciblesolvent is employed it may be employed as such or in the form of anaqueous solution. The amount of water and/ or water-miscible solventemployed is preferably at least sufficient to dissolve the causticalkali and provide a readily stirrable reaction mixture. In general, theefiiciency with which the reduction is promoted increases with anincrease in the concentration of the water-miscible solvent in themixture. Accordingly, in commercial practice it is preferable to employa reduction medium containing at least about 50% by weight of methanolor other water-miscible solvent, based on the content of said solventand water in said medium.

The amount of caustic alkali employed is preferably such as to renderthe reaction mixture strongly alkaline (for example, corresponding witha pH value greater than 12). The concentration of caustic alkali in thereaction medium (water and/or solvent) may vary widely and is preferablybetween 5% and 50% by weight of the sum of the caustic alkali andsolvent therefor (water and/ or organic solvent).

The amount of reducing sugar employed is adjusted according to theextent of reduction desired. I have found that a much smaller amount ofreducing sugar is usually required to effect a particular reduction thanis necessary in the absence of the reduction promoter, as is illustratedin the specific examples below. Thus, as little as onefourth of theamount of reducing sugar which would be required theoretically to reducethe aromatic nitrogen compound, based on the assumption that only thealdehyde '(or keto) group of the reducing sugar is oxidized in thereaction, suffices to accomplish the reduction in Example 4.

The reduction promoter can be incorporated in the reaction medium invarious Ways and at various times. Usually the reduction promoter isemployed as such in forming the reaction mixture. If desired, it may beformed in the reaction mixture or in one of the components thereof; forexample, the sodium bisulfite addition product of 1,4-naphthoquinone canbe preliminarily formed by reacting the naphthoquinone and bisulfite inwater or in methanol, and the resulting mixture can be employed informing the reaction medium for the reduction, similarly to theprocedure disclosed in my Patent No. 2,645,636.

The reduction promoter can be employed in various amounts. It is afeature of the present invention that even small amounts of thenaphthoquinoid reduction promoters are efiective in bringing about thereduction reaction. The minimum amount necessary to produce a ranging inproportions from about li mol' to about mol ofv :naphthoquinoidcompound, :per. nnolof saromatic nitrogencompoundxare usually employed.Generally,.the promoter'etfect-is enhanced by. increasing'the proportionof'naphthoquinoid compound employed and is lessened by reducing theproportion of naphthoquinoid compound employed. Ordinarily, amountsgreater than about molof naphthoquinoid compoundper .mol of aromaticnitrogen compound to be reduced are not advantageous, although they maybe used if.desired,'.since the increased costof the.extra naphthoquinoidcompound is not sufficiently compensated by the additional benefitsderived therefrom to be. of. commercial importance.

The temperature at which the reaction is carried out may varywidely,'and 'is preferably between room temperature (about and 100C.,aboth inclusive. At lower'temperatures' thereaction isslower andrequires costly cooling, while higher temperatures'may require the useof closed vessels and/or promote the formation of relatively largeamounts of primary amines or other by-products.

The process of the present invention is generally applicable to thereduction of various aromatic nitrogen compounds containing nitrogen asa substituent of a benzene nucleus at a higher stage of oxidation thanthe hydrazo stage, and especially water-insoluble (particularly,unsu'lfonated) compounds of this class, such as nitrobenzene,4-chloro-nitrobenzene, 4-nitrotoluene, 4-nitroanisole, 2-nitro-benzoicacid, 4-nitro-benzoic acid, 2-nitro-' benzene sulfonic acid,2,S-dimethyl-nitrobenzene, 3,3- dimethylazoxybenzene, 4,4'dichloro-azoxybenzene and azoxybenzene-4,4'-dicarboxylic acid. Theprocess of the present invention is particularly of value in view of theextensive use of hydrazobenzene and its derivatives, especially thosesubstituted in ortho and meta positions with respect to the hydrazogroup, as intermediates for the manufacture of benzidine and relatedderivatives I of benzidine, especially those containing a halogen atomor an alkyl or alkoxy radical as a nuclear substituent; since itprovides an improved method for manufacturing hydrazo compounds from thecorresponding reducible aromatic nitrogen compounds, such asnitrobenzene, oand m-nitrotoiuenes, Z-nitroanisole, Z-nitrophenetole,2,2-azoxytoluene, 2,2-azoxyanisole, azobenzene, 2,2- azotoluene,2,2-azoanisole, etc., and especially such azoxy and azo compounds.

The process of the present invention is particularly advantageous forreducing Z-halogen nitrobenzenes (e. g., 2-chloro-nitrobenzene and2,S-dichloro-nitrobenzene) and especially reduction products thereof (e.g., 2,2-dichloroazoxybenzene and 2,2'-dichloro-azobenzene), since itpermits a more eificient reduction of such compounds to be obtained andproduces less by-products resulting from replacement of the labilehalogen atoms by OH and OCH3 groups than the processes employing alkalimetal alcoholates; the use of reducing sugars enables the reduction tobe carried out more rapidly and at lower temperatures, therebyminimizing side reactions with said halogen atoms.

The invention will be illustrated by the following specific examples,but it is to be understood that it is not limited to the details thereofand that changes may be made without departing from the scope of theinvention. The temperatures are in degrees centrigrade and the parts areby weight, unless designated as parts by volume in which case the amountsignifies the volume occupied by the same number of parts by weight ofwater at 4 C.

EXAMPLE 1 Part A.-75 parts of dextrose (Cerelose) were added duringabout an hour to a warm (SS-60) mixture of 78.5 parts ofZ-chloro-nitrobenzene, 135 parts of 50 B. aqueous sodium hydroxide, 180parts of water, and 1 part of 2,3-dichloro-1,4-naphthoquinone whilestirring. The resulting mass was heated with stirring to 95-100 and heldthere for 5 hours. The reaction mixture was then steam distilledtofremove the 2-chloro-aniline formed (about 10% :of the theoreticalamount), and the residue was 'allowed'to :cool' to solidify the oil-.as: grains. The grains were filtered off, washed with hotdilutehydrochloric acid'and .thenwith water,:and dried over. calciumchloride in an oven'at'about 100.

The resulting product consisted .of 2,2-dichloroazoxybenzene :mixedwitha considerable amount of 2,2-dichloro-azobenzene (it'had a. settingpoint of 46) and amounted to 56.5 parts, Whichrcorresponds to more than85% of the theoretical yield of'combined dichloro-azoxyanddichloroeazobenzenes,based on the 2-chloro-nitrobenzene charged.

"Part B.-'[he;procedure of Part -A.of this example was repeatedwithout'the. addition of.2,3-dichloro-1,4-naphthoquinone.Theproduct:consistedessgipally of 2,2"-dichloroazoxybenzene (it hadasettingpoint of 54). It Weighed'54 parts, whichtcorresponds to 81% ofthe theo retical yield of.2,2"-dichloro-azoxybenzene.

EXAMPLE 2 Part A.Forty parts of dextrose wereadded with stirring duringabout-1 hour to a warm- (-50") mixture of 66.8 parts of2,2-dichloro-azoxybenzene, 35 parts of flaked sodium hydroxide, 200parts of methanol and 2 parts of 2,3-dichloro-1,4-naphthoquinone, andthe resulting mixture was further agitated at 45-50 for 20 hours. Themass-was then diluted with Water to 500 parts by volume and" filtered,and the filter cake Was washed, first with 100 parts of 10%aqueoushydrochloric acid and then with cold water, and dried.

The product 7 thus obtained consisted essentially of2,2'-dichloro-hydrazobenzene (it had a melting point of 86-87") andamounted to 54 parts, which corresponds to 85% of the theoretical yieldbased on the dichloro-azoxybenzene charged. In addition, some2-chloro-aniline was formed (about 14% of the theoretical yield).

Part B.-When the procedure of Part A of this exampic was repeatedwithout addition of 2,3-dichloro-L4- naphthoquinone, 56 parts of dryproduct were obtained. It consisted of 46% byweight of2,2'-dichloro-hydrazobenzene (corresponding to 41% of the theoreticalyield) and 54% by weight of a mixture of 2,2-dichloro-azoxyand-azobenzenes. In addition, some 2-chloroaniline (about 11% of thetheoretical yield) was formed.

EXAMPLE 3 Table 1 Dry Filter Cake 2,2-Dichl0ro- DON Q, hydrazoben-2-Chlor0aniline, parts zene, Percent Percent theory Parts Percent theoryhydrazo l 0 (control) 38. 2 36. 2 6. 5

lThe hydrazo content was determined by rearrangement to 3,3-dlchloro-benzidine and titration of the latter with nitrous acid. Theremainder of the filter cake was a mixture of 2,2-dichloro-azoxybenzeneand 2,2 -diehloro-azobenzene.

EXAMPLE 4 Part. A.-Thirty-eight parts of dextrose were added to 1 9 awarm 45-50) mixture of 49.5 parts of azoxybenzene; 33 parts of sodiumhydroxide flakes, 220 parts of methanol, and'2 parts of2,3-dichlcro-1,4-naphthoquinone, and the resulting mixture was stirredat 45-50. The reaction was substantially complete in 3 hours (asindicated by production of a white solid) but was left stirringovernight. The mass was then drowned in 1000 parts of cold water. Theresulting precipitate was separated as a cake by filtration, washed withcold water, and dried.

The white product thus obtained consisted essentially of hydrazobenzene(it melted at 126) and weighed 44.5 parts, which corresponds to 98% ofthe theoretical yield of hydrazobenzene, based on the azoxybenzenecharged.

Part B.The procedure of Part A of this example was repeated without theaddition of 2,3-dichloro-l,4-naphtho'quinone. The product obtained asfilter cake consisted of azobenzene and some hydrazobenzene, besidesunreduced azoxybenzene. It weighed 39.5 parts and had the followingcomposition:

EXAMPLE 5 Forty parts of dextrose were added during 2 hours to a wellstirred warm (45-50") mixture of 400 parts of methanol, 50 parts ofsodium hydroxide flakes, 121 parts of 2,2-dimethoxy-azobenzene, and 2parts of 2,3-dichloro- 1,4-naphthoquinone. The resulting mixture wasagitated about 16 hours at 45-50" to complete the reduction, thendiluted with 900 parts of water to precipitate the hydrazo compound, andfiltered. The filter cake was well washed with water and air dried.

The dried product was essentially 2,2'-dimethoxyhydrazobenzene andweighed 122 parts, which substantially corresponds to the theoreticalyield of 2,2'-dimethoxy-hydrazobenzene based on the2,2'-dimethoxy-azobenzene charged.

EXAMPLE 6 Part A.-Fifty-five parts of sodium hydroxide flakes were addedduring about 11 hours to a well stirred mixture, maintained at 40-45, of385 parts of methanol, 70 parts of dextrose, 4 parts of2,3-dichloro-l,4-naphthoquinone, and 133.6 parts of2,2'-dichloro-azoxybenzene (in the form of a filter-cake containingabout of moisture). The resulting mixture was further stirred at 40-45for about 13 hours, then diluted with water to a volume of 1000 partsand filtered. The filter cake was thoroughly washed with water and airdried. The dry product thus obtained was essentially2,2-dichloro-hydrazobenzene (it melted at 86-87) and weighed 116 parts,which corresponds to a yield of 92% of the theoretical based on thedichlor-azoxybenzene charged.

Part B.The procedure of Part A of this example was repeated except thatthe dextrose, rather than the sodium hydroxide flakes, was added to themixture of the other reactants. The yield of 2,2-dichloro-hydrazobenzeneobtained was about 86% of the theoretical (109 parts of product meltingat 86-87).

Part C.The procedure of Part A of this example was repeated except thatthe azoxy compound was added to the mixture of the other reactants. Theproduct weighed 122 parts and was composed of 75% by weight of 2,2-dichloro-hydrazobenzene and by weight of a mixture of2,2-dichloro-azobenzene and 2,2-di-chloro-azoxybenzene (it melted at80-83 The process of the present invention is also of special advantagein connection with the manufacture of 2,2- dialkoxy hydrazobenzenes from2 chloro-nitrobenzene. An economical and efiicient process involvesreacting 2-chloro-nitrobenzene with caustic alkali and a lower alcohol(specifically sodium hydroxide and methanol) in an excess of the alcoholas solvent, whereby the corresponding 2-alkoxy-nitrobenzene(specifically o-nitroanisole) .is formed; adding a small amount of anaphtho quinoidireduction promoter (e. g.2,3-dichloro-1,4-naphthoquinone) and additional alcohol and causticalkali (e. g. methanol and sodium hydroxide) to the resulting reactionmixture and stirring the mixture (with gentle warming if necessary)until formation of the corresponding dialkoxy-azoxybenzene and/ordialkoxy-azobenzene is completed; and then adding a reducing sugar(specifically dextrose) in sufiicient amount to complete the reductionof the azoxy and/or azo compounds to the correspondingortho-dialkoxyhydrazobenzene and continuing the reaction until saidreduction is complete.

This procedure, which is illustrated in the following example, has theadvantage that a high yield of hydrazobenzene compound can be obtained,with relatively low yield of primary amine by-products, by means ofreducing agents much less costly than the zinc and caustic alkaliformerly employed and without requiring a costly separation of zincoxide from the product.

EXAMPLE 7 Part A.--Three hundred and fifteen parts of2-chlorol-nitrobenzene were added to a solution of 128 parts of sodiumhydroxide flakes in 520 parts of methanol. The mixture was stirred forabout 22 hours, during which the temperature was gradually raised from40 to about 65, to complete formation of o-nitroanisole(Z-methoxynitrobenzene) Part B.l60 parts of methanol and 4 parts of2,3-dichloro-1,4-naphthoquinone were added to the mixture thus obtained,after which 150 parts of sodium hydroxide flakes were introduced duringabout 4 hours while stirring and maintaining the temperature at 55-60with cooling. The reaction mixture was then stirred at 55-60 for 16hours to form 2,2'-dimethoxy-azobenzene together with some2,2'-dimethoxy-azoxybenzene.

Part C.To the reaction mixture thus obtained 150 parts of dextrose wereadded during about 4 hours while stirring and maintaining thetemperature at 45-50". This resulted in complete reduction to2,2'-dimethoxyhydrazobenzene. The reaction mixture thus obtained wassteam distilled to remove the methanol, diluted with 450 parts of hotwater, then cooled to 30, and filtered. The filter cake was washedalkali-free with water. When dried,a sample melted at 102. A yield of77% of the theoretical yield of 3,3'-dimethoxybenzidine hydrochloride,based on the 2-chloro-1-nitrobenzene charged, was obtained byrearranging the filter cake of hydrazo compound thus obtained, with acidin the known manner.

As above noted, the invention is not limited to the details of theforegoing illustrative examples and changes may be made withoutdeparting from the scope of the invention.

Thus, other aromatic nitrogen compounds containing nitrogen in areducible form as a substituent in a benzene nucleus, and especiallythose at a lower stage of oxidation than the nitro stage, can besubstituted in place of the specific compounds subjected to reduction inthe foregoing specific examples; for example, nitrobenzene, onitrotoluene, m-nitrotoluene, m-nitrochlorobenzene, pnitrophenetole,p-nitrobenzoic acid, and reduction products thereof, especially,2,2-azoxytoluene, 3,3-azoxytoluene, 3,3-dichloroazoxybenzene and4,4'-azoxy-di benzoic acid and their corresponding azo compounds can besubstituted. I

Further, it is possible to carry the reduction of a v particularreducible aromatic nitrogen compound to other stages than that of aparticular specific example, depending on the nature and amount ofreducing sugar, caustic alkali and naphthoquinoid promoter employed andthe particular reaction condtions, such as concentration ofwater-miscible solvent, temperature, etc. Thus, it is possible to reducea nitrobenzene to a hydrazobenzene in a single reaction mixture;however, it is also possible to reduce the nitro compound to the azoxyand/or azo.

compound in one reaction mixture, isolateuthe :azoxy and/or azo compoundand thenreduce it further with-a fresh charge of reactants in a'separatereactionmixture.

While the nitrogen compound is not reduced to any substantial degree bythe alcohol under the preferred conditions herein employed (since thereducing sugar is a more vigorous reducing agent in the presence ofcaustic alkali than the alcohol, as evidenced by the fact that when theprocedure of Example 2, Part A, was'repeated without the dextrosesubstantially no reduction occurred and 66 parts of2,2'-dichloro-azoxybenzene were recovered), the invention includes aprocedure'and reaction conditions where the alcohol also functions as anauxiliary reducing agent; as for example, when carrying out the processfor prolonged reaction periods at elevated temperatures and inconcentrated alcoholic reaction media.

The products of the reduction can be isolated from the reaction mixturesin any suitable manner. Aside from those cases in which the reactionmixture contains an insoluble residue resulting from the presence of thereduction promoter in the reaction mixture, the isolation of thereduction products can be carried out in the usual manner. For example,the reaction mixture may be cooled to solidify or crystallize thereduction product and filtered, and the filter cake washed with water.In those cases where the product is molten and insoluble in the hotmixture, the mixture can be stratified into an aqueous phase and an oilphase, which can be readily separated as illustrated in theexamples.When a solvent such as methanol is employed, it is preferable to removethe solvent by steam distillation prior to separation of the productfrom the mass. When the use of the reduction promoter produces a smallamount of insoluble by-product, it may be removed by filtering the hotmixtureprior to the phase-separation, or in other suitable manner.

I claim:

1. The improvement in the method of reducing an aromatic nitrogencompound containing nitrogen in a reducible form as a substituent of abenzene nucleus at a higher stage of oxidation than the hydrazo stage byreacting the aromatic nitrogen compound with a reducing sugar and acaustic alkali, which comprises carrying out the reduction in a reactionmedium in which a naphthoquinoid reduction promoter has beenincorporated, whereby the reduction of the aromatic nitrogen'compound ispromoted.

.2. The improvement in the method defined .in claim 1, wherein thenaphthoquinoid reduction promoter. is'a l,4-naphthoquinoid compound.

3. The improvement in the method of effecting the alkaline reduction ofan aromatic nitrogen compound containing nitrogen in a reducible form asa substituent of a benzene nucleus at. a stage of oxidation higher thanthe hydrazo stage and lower than the-nitro stage, which comprisesreacting the aromatic nitrogen compound with a reducing sugar and acaustic alkali in a reaction medium containing a water-miscible organicsolvent and in which a naphthoquinoid reduction promoter has beenincorporated.

4. The improvement in the method defined in claim 3, wherein the solventis a monohyd'ricalcoho'l having I to 3 carbon atoms.

5. The improvement in the method defined in claim 4, wherein the solventis methanol.

6. The improvement in the method definedin claim 5, wherein the reducingsugar is dextrose, the caustic alkali is sodium hydroxide, and thereaction mixture is maintained at a temperature between 30 and 100 C.

7. The improvement in the method of eifecting'the alkaline reduction ofa water-insoluble aromatic nitrogen compound containing nitrogen in areducible form as a substituent of a benzene nucleus at a higher stageof oxidation than the hydrazo stage, which comprises reacting thearomatic nitrogen compound with dextrose and sodium hydroxide in areaction medium which contains a watermiscible organic solvent and inwhich.a.l,4-naphthoquinoidcompound has been incorporated in smallamount.

8. The improvement in the method of effecting the alkaline reduction ofan aromatic nitrogen compound selected from the group consisting ofnitrobenzene,- its ortho-methyl, halogen, methoxy, ethoxy, carboxy andsulfo derivatives, and their reduction products in which the nitrogen isat a higher stage of oxidation than the hydrazo stage, which comprisesmixing together methanol, sodium hydroxide, the reducible aromaticnitrogen compound, and a naphthoquinoid reduction promoter in an aqueousmedium, and adding a reducing sugar to the resulting reaction mixturewhile maintaining the temperature between 30 and C.

9. The improvement in the method of effecting the alkaline reduction ofan aromatic nitrogen compound selected from the group consisting ofnitrobenzene, its ortho-methyl, halogen, methoxy, ethoxy, carboxy andsulfo derivatives, and their reduction products in which the nitrogen isat a higher stage of oxidation than the hydrazo stage, which comprisesmixing together methanol, a reducing sugar, the reducible aromaticnitrogen compound, and a naphthoquinoid reduction promoter in'an aqueousmedium, and adding sodium hydroxide to the resulting reaction mixturewhile maintaining the temperature between 30 and 100 C.

10. The improvement in the method of effecting the alkaline reduction ofan aromatic nitrogen compound containing nitrogen in a reducible form asa substituent of a benzene nucleus at a higher stage of oxidation thanthe hydrazo stage and having a labile halogen substituent, whichcomprises reacting the aromatic nitrogen compound with a reducing sugarand sodium hydroxide in a reaction medium in which a naphthoquinoidreduction promoter has been incorporated.

11. The improvement in the method of eflfecting the alkaline reductionof an aromatic nitrogen compound containing nitrogen in a reducible formas a substituent of a benzene nucleus at a stage of oxidation higherthan the hydrazo stage and lower than the nitro stage and having alabile chloro nuclear substituent, which comprises reacting the aromaticnitrogen compound with sodium hydroxide and dextrose in a reactionmedium which contains a monohydric alcohol having 1 to 3 carbon atomsand in which a naphthoquinoid reduction promoter has been incorporatedin small amount.

12. The improvement in the method defined in claim 11, wherein thealcohol is methanol and'the .naphthoquinoid reduction promoter is a1,4-naphthoquinone.

13. The improvement in the method of reducing an aromatic nitrogencompound containingnitrogen in a reducible form as a substituent of abenzene nucleus at a higher stage of oxidation than the hydrazo stage,but not higher than the azoxy stage, by reacting the aromatic nitrogencompound with a reducing sugar and a caustic alkali, which comprisescarrying out the reduction in a reaction medium comprisinga-water-miscible organic solvent.

14. The improvement in the method defined in claim 13, wherein thearomatic nitrogen compound 'is an azobenzene-and the solvent is amonohydric alcohol having 1 to 3 carbon atoms.

15. The improvement in the method defined in claim 14, wherein thesolvent is methanol.

16. The method of producing v2,2'-.dialkoxy-hydrozobenzenes which.comprises reacting 2-chloro-nitrobenzene with a lower alcohol andcaustic alkali to form the corresponding Z-alkoxy-nitrobenzene, addingto the resulting reaction mixture a naphthoquinoid reduction promoterand reducing theralkoxy-nitrobenzene toat least the correspondingdialkoxy-azoxybenzene stage in said reaction mixture bymeans of alcoholand caustic alkali, and then carrying the reduction 'furtherto thecorresponding dialkoxy-hydrazobenzene in said reaction mixture by meansof a reducing. sugar and caustic alkali.

2,794,047 13 14 17. The method of producing 2,2-dimethoxy-hydrar 18,wherein the naphthoquinoid reduction promoter is zobenzene defined inclaim 16, wherein the alcohol is 2,3-dich1oro-1,4-naphthoquinone.methanol, the caustic alkali 1s sodmm hydroxide and the References Citedin the file of this Patent reducing sugar is dextrose.

18. The improvement in the method defined in claim 5 UNITED STATESPATENTS 3, wherein the reducing sugar is dextrose, the caustic alkali ais sodium hydroxide, the solvent is methanol, and the 0g ynaphthoquinoid reduction promoter is a 1,4-naphtho- OTHER REFERENCESquinoid compound. Rotarski: Chemisches Centralblatt, 76:893-894 (1905).

19. The improvement in the method defined in claim 10 Richter: Textbookof Orig. Chem, 1938 ed., page 64.

1. THE IMPROVEMENT IN THE METHOD OF REDUCING AN AROMATIC NITROGENCOMPOUND CONTAINING NITROGEN IN A REDUCIBLE FORM AS A SUBSTITUENT OF ABENZENE NUCLEUS AT A HIGHER STAGE OF OXIDATION THAN THE HYDRAZO STAGE BYREACTING THE AROMATIC NITROGEN COMPOUND WITH A REDUCING SUGAR AND ACAUSTIC ALKALI, WHICH COMPRISES CARRYING OUT THE REDUCTION IN A REACTIONMEDIUM IN WHICH A NAPHTHOQUINOID REDUCTION PROMOTER HAS BEENINCORPORATED, WHEREBY THE REDUCTION OF THE AROMATIC NITROGEN COMPOUND ISPROMOTED.
 16. THE METHOD OF PRODUCING 2,2''-DIALKOXY-HYDROZOBENZENESWHICH COMPRISES REACTING 2-CHLORO-NITROBENZENE WITH A LOWER ALCOHOL ANDCAUSTIC ALKALI TO FORM THE CORRESPONDING 2-ALKOXY-NITROBENZENE, ADDINGTO THE RESULTING REACTION MIXTURE A NAPHTHOQUINOID REDUCTION PROMOTERAND REDUCING THE ALKOXY-NITROBENZENE TO AT LEAST THE MORRESPONDINGDIALKOXY-AZOXYBENZENE STAGE IN SAID REACTION MIXTURE BY MEANS OF ALCOHOLAND CAUSTIC ALKALI, AND THEN CARRYING THE REDUCTION FURTHER TO THECORRESPONDING DIALKOXY-HYDRAZOBENZENE IN SAID REACTION MIXTURE BY MEANSOF A REDUCING SUGAR AND CAUSTIC ALKALI.